Use of robust multivariate linear mixed models for estimation of genetic parameters for carcass traits in beef cattle

Assumptions of normality of residuals for carcass evaluation may make inferences vulnerable to the presence of outliers, but heavy-tail densities are viable alternatives to normal distributions and provide robustness against unusual or outlying observations when used to model the densities of residual effects. We compare estimates of genetic parameters by fitting multivariate Normal (MN) or heavy-tail distributions (multivariate Student’s t and multivariate Slash, MSt and MS) for residuals in data of hot carcass weight (HCW), longissimus muscle area (REA) and 12th to 13th rib fat (FAT) traits in beef cattle using 2475 records from 2007 to 2008 from a large commercial operation in Nebraska. Model comparisons using deviance information criteria (DIC) favoured MSt over MS and MN models, respectively. The posterior means (and 95% posterior probability intervals, PPI) of v for the MSt and MS models were 5.89±0.90 (4.35, 7.86) and 2.04±0.18 (1.70, 2.41), respectively. Smaller values of posterior densities of v for MSt and MS models confirm that the assumption of normally distributed residuals is not adequate for the analysis of the data set. Posterior mean (PM) and posterior median (PD) estimates of direct genetic variances were variable with MSt having the highest mean value followed by MS and MN, respectively. Posterior inferences on genetic variance were, however, comparable among the models for FAT. Posterior inference on additive heritabilities for HCW, REA and FAT using MN, MSt and MS models indicated similar and moderate heritability comparable with the literature. Posterior means of genetic correlations for carcass traits were variable but positive except for between REA and FAT, which showed an antagonistic relationship. We have demonstrated that genetic evaluation and selection strategies will be sensitive to the assumed model for residuals

Ischemia/reperfusion injury in flow-through venous flaps.

The effects of ischemia/reperfusion (IIR) injury in flow-through venous flaps were evaluated in rabbits. The rates of flap survival and the levels of lipid peroxidation, protein oxidation, and sulfhydryl groups were compared between flow-through venous flaps, conventional flaps after an IIR period (experimental groups), and flow-through venous flaps without being subjected to IIR injury (control groups) in 20 animals. On the seventh day after the onset of reperfusion, 3 of 10 flow-through venous flaps (30%) and 6 of 10 arteriovenous flaps (60%) survived in the experimental groups. Flow-through venous flaps showed a decreased survival rate compared with control and conventional flaps (p < 0.05). Tissue lipid peroxide levels were found to be higher in venous flaps during reperfusion after secondary ischemia (p < 0.05), Tissue protein oxidation and total sulfhydryl groups levels did not show any difference among groups. This study suggests that more free radical damage occurs in flow-through venous flaps during IIR injury